An electromagnetic relay typically consists of an electromagnet block and a contact block. The electromagnet block comprises an iron core, an electromagnetic coil wound around the iron core, a yoke having a first end connected to an end of the core and a second end disposed adjacent to the other end of the iron core, and an armature which can move between a first position to magnetically connect the second end of the yoke and the adjacent end of the iron core, and a second position to open the magnetic connection therebetween. According to a preferred design, the armature consists of a planar member bent into the shape of letter L, having a long piece and a short piece, which rests upon the free end edge of the yoke at its corner portion. The yoke is also formed of a planar member bent into the shape of letter L having a long piece and a short piece.
The magnetic flux conducted through the yoke is then conducted through the short piece of the armature. Since the yoke is typically formed by cutting it out of a planar blank member by means of a punch and die before being bent into the shape of letter L, its edge portion must be properly chamfered appropriately in order to remove burrs and other sources of ruggedness. Therefore, the free end edge of the long piece of the yoke is typically chamfered and the armature rests upon this chamfered free end edge of the yoke, thereby creating a substantially large magnetic resistance.
The armature is also formed from a planar blank member by means of a punch and die, and its edges may have some burrs and other rugged parts. The free end of the long piece of the armature typically bears upon the moveable contact piece of the contact block. Therefore, the uncertainty in the condition of the free end edge of the long piece of the armature could cause a corresponding uncertainty in the stroke of the moveable contact piece.
The armature is typically kept in its pivotally supported position by means of a spring member urging its corner portion against the free end edge of the yoke. Therefore, when an excessive impact is applied to the electromagnetic relay, the supported condition of the armature could become unstable.
Also, the electromagnet block is required to be securely attached to the casing, and this necessitated special securing means, thereby increasing the manufacturing cost.